If Jesus is the only referent discussed in this passage, then Jude's use of "only" may prima facie be slightly problematic since (as subordinationists generally understand the matter) Jesus is not the "only" Lord (strictly speaking) for Christians.
Assuming a subordinationist understanding of matters, I would like to ask whether the word "only" excludes others from serving as lords for Christian followers of Jesus. In other words, does μόνον have to mean that there is no other Lord for the Christian congregation but Jesus Christ? The question is understandable in light of what Revelation 15:4 says about God:
τίς οὐ μὴ φοβηθῇ, κύριε, καὶ δοξάσει τὸ ὄνομά σου, ὅτι μόνος ὅσιος
Yet we also read that an "overseer" (τὸν ἐπίσκοπον) must be ὅσιον (Tit 1:8). Furthermore, Christians are exhorted to lift up "holy hands" (ὁσίους χεῖρας) in prayer to God (1 Ti 2:8).
So the doxological exclamation μόνος ὅσιος (in Rev 15:4) does not mean that others cannot be ὅσιος or live ἐν ὁσιότητι καὶ δικαιοσύνῃ ἐνώπιον αὐτοῦ (Luke 1:75). In fact, we are called to be holy as God is holy.
For the record, one dictionary defines the English word "only" in this way (obviously depending on the context):
"unquestionably the best--PEERLESS; alone in its class
or kind: SOLE
So is Christ the only Lord for Christians? Not according to Psalm 110:1-2 and Acts 2:36. The latter verse teaches that God the Father made Christ the Lord of Christians, but the Father is the ultimate Lord (LORD) of all. The KJV renders the Hebrew letters YHWH (Yahweh or Jehovah) as LORD in Psalm 110:1 and throughout the Hebrew Bible.